The provisions of this section shall be supplemental to any agreement between the retailer and the manufacturer, wholesaler or distributor covering the return of farm implements, equipment, machinery, attachments or repair parts. The retailer can elect to pursue either his contract remedy or the remedy provided herein, and an election by the retailer to pursue his contract remedy shall not bar his right to the remedy provided herein as to those farm implements, equipment, machinery, attachments or repair parts not affected by the contract remedy. Notwithstanding anything contained herein, the rights of a manufacturer, wholesaler or distributor to charge back to the retailer’s account amounts previously paid or credited as a discount incident to the retailer’s purchase of goods shall not be affected. Further, any repurchase hereunder shall not be subject to the provisions of the bulk sales law.